The metro network is mostly a ring network based on synchronous optical network (SONET) or synchronous digital hierarchy (SDH). Ring network has the advantages of simple network architecture, easy to implement add-drop multiplexers (ADM), and high speed protection switching capability to meet the demands of high survival rate. SONET/SDH networks are circuit switch based networks, and are suitable for constant bit rate (CBR) application, such as voice service. However, the circuit switched based network may suffer network resource waste for other applications, such as data service.
In “A summary of the HORNET Project: A Next-Generation Metropolitan Area Network”, White, M. Rogge, K. Shrikhande, and L. Kazovsky disclosed a hybrid optoelectronic ring network (HORNET). HORNET uses the wavelength-division multiplexing (WDM) bi-directional slot ring network architecture of the optical packet switching (OPS) to divide the network nodes into groups. The nodes of a group share an optical wavelength, called home channel of the nodes of the group. Each node has a tunable transmitter and a fixed-tuned receiver of a fixed wavelength, i.e., home channel. FIG. 1 shows an exemplary schematic view of the topology of HORNET.
As shown in FIG. 1, node 1 and node 4 share the purple wavelength λp, node 2 and node 5 share the green wavelength λg, and node 3 and node 6 share the red wavelength λr. In the HORNET architecture, the MAC uses independent control channel for communication and coordination, called distributed queue bidirectional ring (DQBR). DQBR enables the ring network to achieve acceptable network utilization and fairness, and relieves the restriction on the ring network scale.
In the HORNET architecture, the static wavelength distribution manner is used to allocate to the home channel corresponding to each node for receiving packet.
U.S. Pat. No. 6,925,259 disclosed a MAC protocol for optical packet switched ring network. As shown in FIG. 2, the MAC technology uses wavelength stacking to arrange the packets on multiple wavelengths, such as wavelength 1, wavelength 2, and wavelength 3, into a composite packet. The stacking and an admission control with credit-based method are used to transmit data packet. The MAC technology may execute multi-packet transmission. Each node requests to a central admission control node for a transmission quota in advance. When the request is granted, the node may transmit the packets of the quota during per frame period.
The flow size of the data service in recent years has exceeded the voice service, and the difference is growing larger. Therefore, it is imperative to devise a MAC technology suitable for packet-switched metropolitan network with burst traffic to replace the conventional MAC technology of the SONET/SDH network.